Modern fabric trim covers and their interconnected spring and cushion components (collectively termed “upholstery”), such as those used in vehicles, often carefully sculpted and shaped to produce a comfortable and aesthetically pleasing effect. As such, the fabric (typically cloth, vinyl or leather with an appropriate backing material) is secured at many locations along its surface to a resilient or flexible backing that defines the cushioned substrate of the upholstered item (for example, a seat bottom, cushion, back or headrest). The substrate is typically constructed from a resilient material. This resilient/flexible material can be synthetic foam (for example polyurethane and/or isocyanate-based foam) or another cushioning material, such as traditional rubberized horsehair, hog hair, coil springs and the like. In general, the close-fitting appearance of the upholstery to the substrate requires that the fabric be tacked down to the substrate at any intermediate surface contour dips, Vees or trenches in the surface. Otherwise, the fabric will tend to billow out or “tent” at these non-planar surface features.
Trim covers are often secured to resilient substrates using detachable connections that allow repairs to be effected and are often more-easily applied without the used of highly skilled labor. In one example, one side of a hook and loop fastener is attached to a trench in the resilient substrate. The inner surface of the trim cover carries the opposing side of the fastener. This approach is reliable, but expensive, in terms of material wasted and consumed to attain a secure fit. It also requires a rather large-width trench/trough to be formed in the resilient substrate to ensure a sufficient area of engagement between fastener sides. Other approaches can be employed to secure upholstery trim covers to sear cushions but all generally have disadvantages due to complexity in assembly, limitations in service life, etc.
A more effective approach to efficiently and securely attach trim covers to a foam substrate involves the use of resilient polymer trim clips that are embedded in, and adhered to, the foam. With reference FIG. 1, an example of an upholstery clip 100 is shown embedded in a foam substrate 102. The upholstery clip 100 resides within a trench 104 formed in the substrate 102. The clip 100 in this example is a low-profile clip as described in commonly assigned U.S. Pat. No. 8,099,837, entitled LOW-PROFILE UPHOLSTERY CLIP FOR ATTACHING A BEAD TO A FOAM SUBSTRATE, the teachings of which are incorporated herein by reference as useful background information. This exemplary clip 100 includes a planar (flat) rectangular base 110 and an upwardly directed clip member 150 with associated legs 160, and inwardly and downwardly directed barbs 170 adapted to capture a listing bead through a gap 180 therebetween, as described below. The base 110 can define a width (perpendicular to the page of the drawing) of approximately 6 to 9 millimeters with an illustrative value of 7.8 millimeters. The base width is widely variable in alternate embodiments and a wide variation of widths is expressly contemplated beyond the above-specified, exemplary width values. The clip legs 160 have a similar width to that of the base, or are typically narrower than the base width. In general, the base should be wide enough so as to support clip member legs of a desired size. This maintains the strength of the clip member legs. Legs that are too narrow will be more likely to break or fracture during installation of listing or in subsequent field use. By varying the width of (at least) the legs, the performance characteristics of the clip can be varied to accommodate different ranges of push-in and pull-out force, as well as overall load-handling capability. By experimental data, the appropriate width WB of the legs (and optionally the base) can be determined for a given application.
The clip base 110 in this example includes formations 112 and 114 on opposing ends, which are optional and allow for a “festooning” arrangement, wherein clips can be snapped together in a variable-length, flexible chain during storage and distribution by engaging each cylindrical formation 114 with an overlying C-formation 112 on an adjacent clip. Before foam is injected into a mold cavity, the installer peels each clip off of the chain by removing the cylinder formation 114 from an adjacent C-formation 112, and applies it to an appropriate location (e.g. along a trench) within mold cavity. Note that the length LB of the clip base between festooning connectors 112, 114 is highly variable, but is approximately 12-18 millimeters in this example. The thickness TB (FIG. 1) of the base is also highly variable, but is between approximately 1.0 and 2.0 millimeters with an illustrative value of 1.52 millimeters in this example. In general, any clip base herein should have sufficient area to allow it to appropriately adhere to, and become permanently anchored within, the foam substrate free of pull-out under normal loads.
Note also that the base thickness TB can be sized to approximately match (or be greater than) the thickness TL of the legs. Combined with appropriate stress-relieving fillets at the leg roots (interconnections with the base), the overall, substantially uniform thickness of the clip's clamping region (i.e. the legs and intervening base segment) effectively distributes the load from bead-installation flexure and pull-out tension uniformly over the entire clip member structure. This helps to better avoid clip breakage during clip and bead installation and subsequent field use of the installed clip and affords, essentially a C-clamp-effect to the bead by the clip.
FIGS. 2 and 3 show the installation of a typical, prior art listing bead 210 into a low-profile clip in accordance with this embodiment. In FIG. 2, the listing bead 210 is attached at the end of a web 220 (a fabric), which is, itself, attached to an overlying upholstery piece (not shown). The exemplary listing bead 210 of can be formed as a continuous extrusion from an acceptable polymer, and includes a pair of upper walls 230 that are defined at an approximate angle AW with respect to the horizontal line 231. The bead upper walls 230 are arranged to engage the bottom faces 232 of the barbs 170. During assembly, the listing is driven downwardly (arrow 250) toward the gap 180 between the clip member legs/barbs. The maximum width WGB of the listing bead 210 is wider than the width of the gap 180 when the legs are in a resting (unsprung) arrangement. Thus, the listing bead 210 deforms slightly as its rounded lower faces 260 pass through the barbs 170, and the reduced thickness legs 160 flex outwardly (outward arrows 227) in response to the pressure applied by the bead 210 as it engages the rounded ends of the barbs 170.
In FIG. 3, the bead 210 has passed fully through the gap 180 and is now resting (bottomed-out) against the base 110. So long as the central region of the clip is high enough to allow the upper walls 230 of the bead 210 to clear the bottom faces 232 of the barbs 170, then the clip legs 160 are allowed to flex back (inward arrows 320) into their original resting (unsprung) shape. After installation, the natural tension placed upon the attached upholstery covering will generally bias the upper walls 230 of the listing bead into firm engagement with the bottom faces 232 of the barbs 170. This tension, and the relatively close conformance of widths of the clip central region and bead (as shown in FIG. 3), ensures a rattle-free interconnection between the foam substrate and trim cover.
While the above-described, exemplary clip and listing arrangement provides an efficient and reliable mechanism for joining trim covers to foam substrates, it can cause fatigue to workers installing trim covers by hand to the foam substrate. In many applications the use of human installers can be preferred to automated techniques as it allows for more customization and variation in seat designs than is practical when using an automated/robotic assembly system. In particular, the depicted listing bead contains sharp edges (i.e. corners 290 in FIG. 2) on its upper surface that dig into the installers fingers as he or she applies assembly pressure to drive the bead into the clip(s). This can limit a worker's time on the assembly line and otherwise cause undesired discomfort.